345D, 349D and 349D2 Excavators Hydraulic System Relief Valve (Main) - Test and Adjust - Heavy Lift Caterpillar

1. Position the machine on level ground and stop the engine.

2. Release the pressure in the hydraulic system. Refer to Testing and Adjusting, "Hydraulic System Pressure - Release".
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   Illustration 1	g01229149
   Pump compartment (1) Pressure tap (pressure for drive pump) (2) Pressure tap (pressure for idler pump)

3. Attach a 60000 kPa (8700 psi) pressure gauge to pressure tap (1) and pressure tap (2).

   Note: Certain machines will default to "Economy Mode" at machine startup. Change to "High Hydraulic Power Mode" before performing the test procedure.

4. Start the engine.

5. Exit the service mode.

6. Place the machine controls at the following settings: engine speed dial "10" and AEC switch OFF. Refer to Testing and Adjusting, "Engine Performance - Test (Engine Speed)" for engine rpm settings.
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   Illustration 2	g01229152
   (3) Heavy lift switch

7. Set heavy lift switch (3) to the ON setting. Make sure that the indicator light is on.

8. Increase the hydraulic oil temperature to 55° ± 5°C (131° ± 9°F).

9. Raise the boom until the boom cylinder rods are at full extension.

10. Check the main relief valve pressure setting at pressure tap (1) and pressure tap (2).

11. Return the joystick for the boom to the NEUTRAL position.
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    Illustration 3	g01229155
    (4) Heavy lift relief locknut (5) Heavy lift relief adjustment screw (6) Standard main relief locknut (7) Standard main relief adjustment screw

12. The relief valve pressure setting for heavy lift should be 38000 + 500 - 1000 kPa (5510 + 73 - 145 psi). If the relief valve pressure setting for heavy lift is not within the specification, adjust the relief valve pressure setting for heavy lift.

    1. Loosen locknut (6) in order to adjust standard main relief valve (7). Tighten standard main relief valve (7) until the valve stops turning. Tighten locknut (6).

    2. Loosen locknut (4) in order to adjust the relief valve for heavy lift. The main relief valve is located on top of the main control valve. Adjust the pressure by turning the heavy lift adjustment screw (5) until the pressure gauge reading at pressure tap (1) is 38000 + 500 - 1000 kPa (5510 + 73 - 145 psi).

       Note: Turning adjustment screw (5) clockwise increases the pressure. Turning adjustment screw (5) counterclockwise decreases the pressure.

    3. Tighten locknut (4) to a torque of 75 ± 10 N·m (55 ± 7 lb ft).

       Note: Confirm the heavy lift pressure by fully retracting the stick cylinder.

13. Set heavy lift switch (3) to the OFF setting. The indicator light should not be illuminated.

14. Open the bucket until the bucket cylinder rod is at full retraction.

15. Check the main relief valve pressure setting at pressure tap (1).

16. Return the joystick for the bucket to the NEUTRAL position.

17. The main relief valve pressure setting should be 35000 + 500 - 1000 kPa (5075 + 72 - 145 psi). If the main relief valve pressure setting is not within the specification, adjust the main relief valve pressure setting.

18. In order to adjust the main relief valve, loosen locknut (6) and turn adjustment screw (7) until the pressure gauge reading at pressure tap (1) is 35000 + 500 - 1000 kPa (5075 + 72 - 145 psi).

    Note: Always make final pressure adjustments on pressure rise.

19. Tighten locknut (6) to a torque of 50 ± 10 N·m (37 ± 7 lb ft).

Temporary Setting of the Main Relief Valve

Note: To adjust line relief valve pressure settings, the main relief valve must be temporarily adjusted to a higher setting since the line relief valve pressure settings are higher than the main relief valve pressure setting.

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Illustration 4	g01229152
(3) Heavy lift switch

1. Set the heavy lift switch (3) to the ON setting. Make sure that the indicator light is ON.

2. The main relief valve pressure setting should be 38000 + 500 - 1000 kPa (5510 + 73 - 145 psi) when the heavy lift mode is on. If the main relief valve is not within the specification, adjust the main relief valve pressure setting to the correct pressure specification before performing Step 3. Refer to Testing and Adjusting, "Relief Valve (Main) - Test and Adjust (Heavy Lift)".
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   Illustration 5	g01229155
   (4) Heavy lift relief locknut (5) Heavy lift relief adjustment screw (6) Standard main relief locknut (7) Standard main relief adjustment screw

3. Loosen locknut (6) and tighten screw (7) until no adjustment is left.

4. Tighten locknut (6) while screw (7) is secured.

5. Loosen locknut (4).

6. Tighten screw (5) until the pressure reading of tap (1) or (2) will not rise more. Read the pressure of tap (1) or (2).

7. Turn screw (5) clockwise by a quarter turn. Tighten locknut (4) while screw (5) is secured.

8. Perform the desired steps for testing and adjusting the line relief valves.

9. Reset main relief valve pressure setting to the normal operating condition. Refer to Testing and Adjusting, "Relief Valve (Main) - Test and Adjust (Heavy Lift)".